1. Field of the Invention
The current invention relates to liquid crystal display (LCD) devices that use a light source for viewing of an image. More particularly, the invention relates to a method and apparatus for enhancing an image displayed on a LCD panel illuminated by a lighting device.
2. Background Information
Various liquid crystal display (LCD) devices use a lighting source to either project an image onto a display surface such as a screen or have the light source positioned behind the LCD panel for direct viewing of an image produced on the LCD panel. A desire to reduce power consumption and improve the contrast of images displayed by LCD technology has led to various techniques for dynamically varying the light intensity of the light source and/or backlight of such LCD devices. Typically such variations in intensity of the light source results in a net dimming of the displayed image below the light intensity at which it was designed to be viewed.
In order to overcome this problem various compensation techniques have been proposed for an image being displayed. Techniques such as those described in U.S. patent publications 2006/0268180 and 2007/0092139 use tone-scale mapping to compensate the video signal for lower backlight intensity. These tone-mapping techniques utilise histogram analysis of the video image which requires high real-time computing power. Tone mapping is also suitable for whole backlight dimming, but is less suitable for dynamic and localised dimming techniques.
Another technique has been proposed in U.S. 2007/0041636 which utilises two sequential mapping functions. A first mapping value is determined by substituting RGB values into the first mapping function and a second enhanced mapping value is obtained by substituting the first mapping value into the second mapping function. Again such a technique has a high real-time computational overhead and while being suitable for whole backlight dimming is not a suitable for dynamic or localised dimming techniques.